Art of converting hydrocarbon oils



June 16, 1936. .!.Y K. ROBERTS I ART OF CONVERTING HYDROCARBON OILS Filed May 31, 1933 INVENTOR 0SEPH It ROBERTS ATTORNEY Patented June 16, 1936 2,044,636 ART or convan'rmc nrnaocon OILS Joseph K. Roberts, 1

Standard Oil Com 1111., a corporation of Application y 311, N33,

My invention relates generally to the produc-' tion of low boiling hydrocarbon oils from higher boiling ones and more especially to a process in which the capacity of the system is increased 5 with a maximum yield of a high anti-knock gasoline, without the formation of objectionable 10 different viscosities may be separately cracked.

One'stream of oil to be used as the original charge to the system, in the nature of a dirty gas oil or reduced crude, may be separately heated to a light. cracking temperature and there- 15 after passed to a separate zone wherein it may be digested or soaked to continue the desired conversion. A second stream of oil, in the nature of a clean reflux condensate, may be subjected to vapor phase cracking conditions in a separate 20 heating coil and thereafter passed to a digesting or soaking zone in vapor form wherein the conversion thereof may be continued. The vapors resulting from both the liquid phase and the vapor phase soaking operations, together with 25 remaining. unvaporized oil from the liquid phase soaking operation, may be passed to another zone wherein additional vaporization takes place and the total vaporous constituents scrubbed and cooled to produce a vapor fraction that may be 80 further fractionated to separate therefrom a reflux condensate of desired color and end point and a final overhead distillate of a high antiknock rating.

An important feature of my invention may be 86 to utilize the lightly cracked charging stock as ;a flushing medium to prevent coke deposition in the lower portion of the vapor phase so I chambers. In order to make myinvention more clearly 4 understood, 1, have vshown in the accompanying drawing a ,diagrammatic elevatlonal view of an apparatus suitable for carrying out my invention, the embodiment sho being merely for carry- 25 ing the invention into practical eflect without limiting the improvements intheir useful application to the particular construction which, for

the purpose of explanation, has been made the subject of illustration.

Referring to the drawing, I have shown a fur- 50 nace I provided with a bridge wall and having a convection coil 2 and'a radiant coil 8 positioned therein. The numerals 4 and 6 indicate enlarged chambers for use as vapor phase digest or soaking drums. The numeral 6 indicates a chamber which may be usedv as a liquid p assignmto Qhlcago.

digesting or sea drum. The numeral l in= dicates a vessel which may be operated m a combined scrubbing and fractionating r The numeral 8 indicates a suitable dephlegmating column, such as a conventional bubble tower, 0 5 a reflux condenser associated with the bubble tower 8, ii a condenser cooled by any suitable cooling fluid and i2 a gasoline distillate receiver.

The various enlarged vessels may be insulated against heat loss. The apparatus shown is mere- 10 Ly for illustrative purposes and any suitable type may be employed.

Fresh charge, in the nature of a dirty gas oil or reduced crude, may be forced through a line l3 by means of a pump it into a coil it posltioned in the reflux condenser 9. The fresh charge passing through the coil it may be preheated by indirect heat exchange with vapors passing through the reflux condenser. The preheated fresh charge after through the coil it may be conducted by means of a line It through a heat exchanger II wherein it may be further heated by indirect heat exchange with a portion of the reflux condensate from the bubble tower 8, the formation of which will later be explained. The charge may then be passed through the coil 2 positioned in the convection heating section of the furnace l and then to a section of coil I8 positioned against the bridge wall of the furnace and heated by radiant heat. The charge in passing through the coils 2 and is may be heated to a light cracking temperature without excessive formatlon'and deposition of Yearbon within the conduit elements. The lightly cracked charge may then be passed through a transfer line 2i into the vessels 4 and 5 by means of valved lines 22 and 23.

In accordance with my invention, an exceptionally clean reflux condensate is formed in the bubble tower t and forced through a line 2% 40 by means of a high pressure pump 25 through the radiant heating coil 3 wherein it is subjected to vapor phase cracking conditions. The reflux condensate passing through the radiant coil 3 may be subjected to a high rate of cracking per thereby improving the antiknock properties of the gasoline distillate ultimately obtained. The highly cracked vapors may be passed from the radiant cracking coil t through a vapor transfer .llne 28 into the enlarged crs t and 5 by means of valved pl 21 and 28, respectively.

' The vapors entering the enlarged chambers l and I flow downwardly in parallel and are fur thcr converted or cracking conditions. In order to equalize temperature and pressure conditions prevailing in the enlarged chambers 4 and 5, a crossover line 29 connecting these two chambers may be provided, if desired.

The vapors afterbeing further cracked in the enlarged chambers 4 and 5 may join the heated fresh charge introduced into the lower portions of these vessels and provide additional heating of the fresh charge by direct contact therewith. The combined vaporous and liquid products may be withdrawn from the enlarged chambers 4 and 5 through valved outlet lines 31 and 32 connected to a manifold line 33. The fresh charge being introduced into the lower portions of the enlarged chambers 4 and 5, may be eilectively utilized as a flushing medium to wash out the bottom outlets 3i and 32 in order to prevent any material or excessive accumulation or deposition of carbon therein.

The enlarged chambers 4 and 5 may, in accordance with my invention, be operated in such a manner as to prevent the accumulation of liquid therein. The liquid oil may be constantly withdrawn from these vessels through the outlet lines 3i and 32 at a rate adequate to prevent the accumulation of any substantial amountof liquid v therein. The highly cracked vapors may be maintained in the enlarged chambers for a sufficiently long period to accomplish the desired conversion thereof at substantially the same superatmospheric pressure as that-obtaining'in the heating coil 3. It is preferred not to drop the pressure maintained on the oil in the en-.- larged chambers, but this pressure may be dropped, if desired.

The streams of combined vaporous and liquid constituents may then be passed through the manifold line 33 into the upper portion of the enlarged chamber 6, wherein a high liquid level may be maintained by any suitable type of float mechanism not shown and a large body of liquid digested at cracking temperature. The contacting of the fresh charge with the highly heated vapors produces additional cracking of the fresh charge. The vaporous constituents of the combined stream, together with entrained liquid particles, and additional vapors produced by the vaporization of the liquid constituents, may be removed from the enlarged chamber 6 through a vapor line 34. The unvaporized or liquid constituents in the enlarged chamber 6 after the desired digestion thereof may be removed through a line '35 which may be connected to the line 34 by means of a common manifold line 36. The float mechanism may be connected to a suitable valve positioned in the line 35 for actuating it to'm'aintain the desired liquid level.

In lieu of maintaining a high liquid level in.

the enlarged chamber 6, substantially no liquid level may be held therein. In this manner of operation, the liquid constituents are withdrawn through the outlet line 35' at a rate adequate to prevent the accumulation of any liquid therein and the vaporous products may be withdrawn through the line 34.

The combined liquid and vaporous constituents may be introduced into the enlarged chamber I through the line 33 wherein the liquid constituents may be further vaporized and the combined highly cracked vapors and the vapors resulting from the charge subjected to a primary scrubbing and iractionating operation wherein undesired constituents are removed and avapor fraction I o! the desired end point and color obtained. In

order to obtain an exceptionally clean vapor fraction from the enlarged chamber 1, suitable bubble trays and batlles may be positioned therein and a cool refluxing medium contacted with the vapors.

In accordance with my invention, a portion of the reflux condensate formed in the bubble tower 8 may be used as a cooling medium for the upwardly rising vapors in the chamber 1. As illustrated, a portion of the reflux condensate may be withdrawn from the lower portion of the bubble tower 8 through a line 31, by means of a pump 38 and forced into the heat exchanger l1. The

reflux condensate passing through the heat exchanger ll loses part of its heat by indirect heat exchange with the fresh charge passing therethrough. In order to further cool the reflux condensate, it may be passed through a second heat exchanger 4| wherein it maybe brought into heat exchange with any suitable cooling medium, such as water or oil. The cooled reflux condensate may then be passed through a .line 42 and introduced into the upper portion of in the bottom of the chamber 1 may be removed by means of a line 40 and passed to a tar stripping plant.

The vapors introduced into the bubble tower 8 may be subjected to further fractionation to form an overhead distillate product and a liquid constituent which may be collected'in the bottom of the bubble tower. The vaporous constituents may then be conducted through the reflux condenser 9 wherein additional heavy constituents present in the vapors passing therethrough may be'removed by indirect heat exchange with the fresh charge passing through the coil l5. The liquid particles condensed from the vapors passing through the reflux condenser may be returned to the bubble tower 8 and utilized as a refluxing medium therein, the liquid particles flnally collecting in a pool in the bottom. The liquid collected in the bottom of the bubble tower 8 is a clean reflux condensate and may be satisfactory to be returned to the radiant heating coil 3 as hereinbefore described and therein subjected to a high crack per pass without detrimental gas and carbon formation. 1

The desired vaporous products from the reflux condenser 9 may be conducted through a, pipe 45 to the condenser H wherein they may be condensed into a liquid distillate. The liquid distillate in the nature of a high anti-knock gasoline leaving the condenser ll may be passed through a line 45 to the gasoline distillate receiver l2, which may be provided with a valved gas outlet 41 and a valved liquid distillate drawoff 48.

In some cases, more particularly when'maintaining a large body of liquid in the chamber 6, a portion of the reflux condensate being used as a refluxing medium in the chamber 1 may advantageously, in accordance with my invention, be utilized to prevent cokingof tne liquid drawofl line 35. As illustrated, a valved line 49 may be branched oil! of the line 42 and passed through 75 2,0,oec

the lower portion of the enlarged chamber d, preferably near the outlet line 35. By passing a portion of the cooled reflux condensate in the manner described, I have found that coke troubles ordinarily experienced in drawing oil be substantially eliminated.

In order to further increase the capacity of the system and provide additional cooling for the bubble tower 8, still another portion of the reflux condensate passing through the heat exchangers l'l and iii may be advantageously utilized to cool the vapors passing through the line t l. In accordance with my invention, a valved line 5!! may be branched ofi of the line 32 and connected to the vapor line it for introducing a portion of the cooled reflux condensate into the vapors in order to cool them. I have found stituents may be removed from the vapors thereby without the necessity of the vapors passing through all or a portion of the bubble towerand reflux condenser.

Superatmospheric pressure may be maintained throughout the system. The bubble tower u may be maintained at a lower superatmospheric pressure than the preceding part of the cracking system. To accomplish the desired reductionoi pressure, a valve 52 may be placed in the line at. I may, for example, operate the bubble tower at 200 pounds per square inch with the preceding part of the combination liquid and vapor phase system operated at 300 pounds per square inch. These pressures are merely examples in which satisfactory operation may be accomplished and it is to be understood that any suitable superatmospheric pressure may he maintained throughout all or various parts oi. the system.

in an-example in accordance with my havention, fresh charge such as reduced crude in the nature oia black oil may be forced at a rateoi 150 barrels per hour through the reflux condenser d and the heat exchanger iii and heated to a temperature oi about 500 F, The preheated charge may then be passed through the coils t and it wherein it is raised to a temperature oi about too F. Reflux condensate from the bubble tower at about a temperature oi 700 F. may be forced at a rate of about 250 barrels per hour through the radiant coil 3 and therein subjected to vapor phase cracking conditions at a temperature of about 925 to 950 F. and at a pressure oi about 300 pounds per suuare inch.

The highly cracked vapors from the coil i y be introduced into the upper portion of the en larged chambers i and 5 and therein stained at the approximately same superaospheric pressure for a period suciently long to suit stantlally complete the desired conversion thereof. The vapors may be digested in the chem hers i and d at a temperature oi about are to our l 'i 'hevapors may then be combined in the lower portion of the enlarged vessels th the lightly cracked fresh charge and conducted to the en larged chamber t. The combined streams may be at a temperature of about 890 to til? ii and the liquid may be constantly is, to e-1 vent accumulation therein.

The combined vaporous and liquid constituents may be separated in the chamber t, the vapors being withdrawn and the liquid maintained therein to accomplish further conveon thercoi.

hot oil may flux condensate at a temperature of about 250 F.

may be passed through the line it and utilized as a cooling medium. The resulting vaporsat a temperature of about 780 to 800 F., together with a portion of the reflux condensate introduced through the line ti may be further fractionated and vaporized at a pressure of about 200 pounds and a final vapor fraction having an end point of 400 F. passed to the condenser l i.

In operating in accordance with the aboveconditions, a gasoline distillate having an octane number of 75.5 to 77 by the C. F. R. research methods was recovered in the receiver it.

In practicing the invention, it is preferred to subject the cycle condensate in transit through the coil i to more extensive cracking than that to which the black oil or relatively dirty stock is subjected in the coils 2 and il. 'For example, the clean cycle condensate may be subjected in the heating coil to a cracking per pass of 15 to 20% while the dirty stock may be subjected to a cracking per pass amounting to less than 10% in the heating coil. The two streams of oil which have thus been subjected to diderent extents of cracking may then be combined for further digestion at cracking temperature in the mixed phase.

cracking temperature under conditions to subject said cycle'condensate to a higher rate oi cracking per pass so that it is more extensively cracized than said trash charging stock in said first named heating coil, directing the highlyheated extensively cracked cycle condensate to an upper portion off an enlarged reaction chamtill her maintained at cracking temperature wherein cracking is continued on the cycle condensate products flowing downwardly therein, introducing the lower temperature less extensively cracked fresh charging stocic'at cracking temperature into the bottom portion of said enlarged reaction chamber near the outlet thereof and into contact with the higher temperature products oi reaction of the cycle condensate, immediately thereafter withdrawing the commingled products comprlsi vaporous and liquid products undergoing reaction from the bottom of the enlarged reaction chamber at a rate adequate to prevent the accumulation of liquid therein, passing the withdrawn products into another enlarged reaction chamber maintained at cracking temperature under super-atmospheric pressure wherein close is continued, removing products of reaction irom the latter enlarged reaction chamber iractio themto torm distillate product.

2. The process of cracking hydrocarbon oil -that comprises passing fresh charging stock through a heating coil and heating it therein to a cracking temperature under superatmospheric pressure to subject it to a moderate rate of cracking per pass, passing cycle condensate through a separate heating coil and heating it therein under superatmospheric pressure to a higher cracking temperature under conditions to subject said cycle condensate to a higher rate of cracking per pass so that it is more extensively cracked than said fresh charging stock in said first named heating coil, directing the highly heated extensively cracked cycle condensate to an upper portion of an enlarged reaction chamber maintained at cracking temperature wherein cracking is continued on the cycle condensate products flowing downwardly therein, introducing the 'lower temperature less extensively cracked fresh charging stock at cracking temperature into the bottom portion of said enlarged reaction chamber near the outlet thereof and into contact with the higher temperature products of reaction of the cycle condensate, immedi-. ately thereafter withdrawing the commingled products comprising vaporous and liquid products undergoing reaction from the bottom of the enlarged reaction chamber at a rate adequate to prevent the accumulation of liquid therein, passing the withdrawn products into another en'- larged reaction chamber maintained at cracking temperature under superatmospheric pressure wherein cracking is continued, removing products of reaction from the latter enlarged reaction chamber at a rate adequate to prevent the accumulation of liquid therein and fractionating them to form aforesaid cycle condensate and the desired distillate'product.

3. Theprocess of cracking hydrocarbon oil that comprises passing fresh charging stock through a heating coil and heating it therein to a cracking temperature under superatmospheric pressure to subject it to not more than 10% cracking per pass, passing cycle condensate through a separate heating coil and heating it therein under superatmospheric pressure to a higher cracking temperature under conditions to subject said cycle condensate to a higher rate of cracking per pass of from 15 to 20% so that it is more extensively cracked than said fresh charging stock in said first named heating coil, directing the highly heated extensively cracked cycle condensate to an upper portion of an enlarged reaction chamber maintained at cracking temperature wherein cracking is continued on the cycle condensate products flowing downwardly therein, introducing the lower temperature less extensively cracked fresh charging stock at cracking temperature into the bottom portion of said enlarged reaction chamber near the outlet thereof and into contact with the higher temperature products of reaction of the cycle condensate immediately thereafter, withdrawing the commingled products comprising vaporous and liquid products undergoing reaction from the bottom of the enlarged reaction chamber at a rate adequate to prevent the accumulation of liquid therein, passing the withdrawn products into another enlarged reaction chamber wherein cracking is continued, maintaining a relatively large body of liquid in the latter enlarged cracking chamber at a cracking temperature under superatmospheric pressure, removing all the products of reaction from the latter enlarged reaction chamber and passing them into a separating chamber wherein separation of vapors from residue occurs and subjecting the separated vapors to fractionation to form the aforesaid cycle condensate and the desired distillate prod-' JOSEPH K. ROBERTS. 

